HD24tools stores some settings in a preferences file for your convenience. For instance, the last used device, project directory etc. will be stored in there. Unfortunately, under some unforseen circumstances, HD24tools may not be able to restore settings from that file and may fail to start up, even after re-installing it. If you experience this, you can likely resolve this problem by deleting the preferences file.
The preferences file is called HD24tools.prefs and it is generally tucked away somewhere in the home folder of the user running it. Under Windows, you'll find it under Documents and Settings\(username)\HD24\HD24tools.prefs; under Linux (and probably on Mac), it will be in the home directory under .fltk/HD24/HD24tools.prefs. If you are running as root or as administrator, the settings file will be under the root/administrator home folder.
Regardless of where it is stored, you should be able to find the preferences file by doing a system-wide search for it.